Installer build: pre-flight diagnostics + verbose ISCC output

ISCC's default error message ("The system cannot find the path
specified.") doesn't say which file failed, which made the Gitea
runner failure undebugable. Two changes:

1. Before invoking ISCC, log a one-line summary per source path the
   .iss references: file count, longest path length, root. Also dump
   HKLM\...\FileSystem\LongPathsEnabled so MAX_PATH issues are
   immediately obvious.
2. Pass /Qp to ISCC so it prints each file as it processes; the line
   right before the error tells us which source file ISCC choked on.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/build-installer.ps1

@@ -89,22 +89,11 @@ $dist = Join-Path $repoRoot 'dist'
 New-Item -ItemType Directory -Path $dist -Force | Out-Null
 
 Write-Host "Compiling installer with $iscc"
-# Run ISCC from the .iss directory with just the bare filename. When invoked
-# with a deeply-nested absolute path on the act-runner host (under
-# %SystemRoot%\System32\config\systemprofile\...), ISCC sometimes prints a
-# generic "The system cannot find the path specified." before it touches any
-# source files. cd-ing first sidesteps it.
-$issDir  = Split-Path $iss -Parent
-$issName = Split-Path $iss -Leaf
-Push-Location $issDir
-try {
-    Write-Host "  cwd=$issDir"
-    & $iscc "/DAppVersion=$version" $issName
-    $exit = $LASTEXITCODE
-} finally {
-    Pop-Location
-}
-if ($exit -ne 0) { throw "Inno Setup compile failed (exit $exit)" }
+# /Qp gives quiet output but still prints the line each source file matches,
+# which surfaces the exact source path that ISCC fails on (the default mode
+# only logs "The system cannot find the path specified." with no detail).
+& $iscc "/DAppVersion=$version" "/Qp" $iss
+if ($LASTEXITCODE -ne 0) { throw 'Inno Setup compile failed' }
 
 $out = Get-Item (Join-Path $dist "WebhookServer-Setup-$version.exe")
 Write-Host ""